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I'm all for installing air filters in classrooms for a number of reasons, but I also think the extreme results from this study aren't going to hold up to further research.

From the paper:

> To do so, I leverage a unique setting arising from the largest gas leak in United States history, whereby the offending gas company installed air filters in every classroom, office and common area for all schools within five miles of the leak (but not beyond). This variation allows me to compare student achievement in schools receiving air filters relative to those that did not using a spatial regression discontinuity design.

In other words, the paper looked at test scores at different schools in different areas on different years and assumed that the only change was the air filters. Anyone who has worked with school kids knows that the variations between classes from year to year can be extreme, as can differences produced by different teachers or even school policies.

Again, I think air filtration is great indoors, but expecting test scores to improve dramatically like this is not realistic. This feels like another extremely exaggerated health claim, like past claims made about fish oil supplements. Fish oil was briefly thought to have extreme positive health benefits from a number of very small studies like this, but as sample sizes became larger and studies became higher quality, most of the beneficial effects disappeared.

I wish there was more data on the effects of gasses in the air on people.

We seem to know:

- Elevated CO2 in rooms impairs cognitive performance.

- Elevated CO2 in submarines, at levels far higher than you would see in a normal room does not appear to impact cognitive performance.

- Installing carbon filters (what this study actually looked at) might improve classroom performance.

- People don’t like stuffy rooms.

All this is consistent with multiple hypotheses. It could be that we just don’t know anything about it. Or maybe there is some gas or gasses emitted by people that isn’t CO2 that makes people mildly uncomfortable and have worse cognitive performance.

CO2 is certainly a good proxy for ventilation quality in a space where air is exchanged with outdoors but where the gasses in the air are not otherwise changed. Carbon-filtered classrooms and submarines are not examples of this.

Someone writes whether the data actually shows what it purports to show: https://statmodeling.stat.columbia.edu/2020/01/09/filters-be...

> The whole thing is driven by one data point and a linear trend which makes no theoretical sense in the context of the paper (from the abstract: “Air testing conducted inside schools during the leak (but before air filters were installed) showed no presence of natural gas pollutants, implying that the effectiveness of air filters came from removing common air pollutants”) but does serve to create a background trend to allow a big discontinuity with some statistical significance.

I’m reminded of the walkback of scientific studies showing massive benefits from giving kids in third world countries deworming medications: https://www.theguardian.com/society/2015/jul/23/research-glo....

My beef with Matt Y.’s worldview of “scientifically driven public policy” is that the costs and benefits of public policy interventions are so devilishly difficult to study that you can’t meaningfully use them on realistic time scales to drive policy. This is an exceedingly simple hypothesis—filtering air improves test scores—that can easily be tested while controlling for confounding factors. But even then it’s hard!

Anecdote: Our daycare was a plague ship right after covid 'ended'. None of the kids had any immunities, and they made up for it in a hurry. Man, what a terrible year.

As a result, the daycare got a grant to get N-95 air filters installed and those UV lights that Chinese restaurants tend to have in the bathrooms. One per room.

What. A. Difference.

The infants and kids coming up are not nearly as sick, and when they do get sick, it's not nearly as terrible. The RSV vaccine has also been a godsend.

I can't really tell/feel what what the silver bullet here, but the combinations have been amazing. So much so that we got them for the house.

I’m so confused why they installed HEPA filters to filter out LNG and methane.

And HEPA filters don’t really scrub CO2 that effectively, even with a carbon membrane, so can we really expect lower CO2 levels?

Considering this, what’s the actual takeaway here? Cleaner air (dust/virus free?) is better for productivity?

I am asking because I want to buy the same filter for work, but I am doubtful that the $700 HEPA filter sounds like the same filter they used, even though the article mentions they used readily accessible 5 stage filters.

>For a sense of scale, Mathematica Policy Research’s best evidence on the effectiveness of the highly touted KIPP charter school network finds that after three years at KIPP there is significant improvement on three out of four test metrics — up 0.25 standard deviations on one English test, 0.22 standard deviations on another, and 0.28 standard deviations on one of two math tests.

I wasn't sure what .22 std deviations meant, so I looked stuff up a bit. For a normal distribution, going from the average to 1 standard deviation above is going from the 50th percentile to the 84th percentile. Going up .22 standard deviations from the average is going from the 50th percentile to about the 55th percentile.

Only marginally relevant, this is one reason I use swamp coolers in my home. My windows are open 24/7, 4 months of the year. I hear the birds in the morning and it’s so much more pleasant than shutting in an air conditioned box, in my opinion

Related. Others?

A review of the effects of installing air filters in classrooms - https://news.ycombinator.com/item?id=22006595 - Jan 2020 (26 comments)

Installing air filters in classrooms has large educational benefits? - https://news.ycombinator.com/item?id=22006033 - Jan 2020 (48 comments)

I wonder how smart I’d be if I didn’t sit in a classroom full of metal tables that got painted with such a thick layer of oil paint that it stunk of paint thinner until Spring

What are they "filtering"? You can filter particulates, but methane removal is more complicated.

Makes sense

Personal anecdote getting an airthings that reminds me to open the window (along with a pushover api setup) has probably been the biggest productivity improvement in 10 years.

Also, turns out preventing kids from getting sick improves educational outcomes.

Many air filters are generating annoying sounds. You get better air, but the distraction by the constant noise of the filter might be more than counter productive.

Does anyone have any details on what kind of filter this was? I bought a relatively high-MERV filter for my home, but I’m wondering what I should actually be trying to filter out.

A study published just yesterday [1] showed that just two airborne diseases [2] were responsible for approximately 85% of all sicks days in Greece during 2023-2024. Disregarding the common-sense argument that reducing collective suffering is a good thing overall - even by the cold hard logic of capital, being able to reduce company sick days by up to 85% is a huge opportunity.

Imo we're way overdue standards and controls for clean indoor air that are on par with standards for drinking water and food. Like this article shows, we have the tech to provide clean air today. All we're missing is policy to uniformly deploy it.

[1]: https://www.sciencedirect.com/science/article/abs/pii/S01966...

[2]: SARS-CoV-19: ~75% of sick days, Influenza: ~10% of sick days

There have been some classroom studies in the UK showing a reduction in illness as well. They were a bit better run than this because they had some some pupils in filtered air and some not and even with the mixing at break time the reduction of illness met clinical significance. Given Covid is doing its thing all year around its quite an easy thing to do to drastically reduce the time teachers and pupils spend away from school and its a fairly easy measure to adopt. They do need to have the filters running however and that will involve explaining to the teachers how they work and why they are needed because in a lot of studies compliance has been a big issue usually due to misinformation rather than issues with the devices.

i'm sure it's because they were white noise generators essentially.

Given that SARS2 affects cognition negatively, I would expect schools with universal air filtration to have larger improvements than we would have expected prior.

Now let's see if the filters are not changed in a while, and how that effects the studies (not on purpose, I'm guessing that the upkeep is not very good with filters in general)

From 2020.

There are well established hierarchies of evidence in health studies and this study would rank as low quality evidence due to inability to control for other factors. See https://gdt.gradepro.org/app/handbook/handbook.html#h.3183vu... for background.

In studies of pollution and impacts on health, the confounding factors often have a larger impact on the health outcome than the pollutant, such as particulate level, and therefore significant control of confounders is required to estimate any impact on the health outcome. The strong effect in this study is highly suggestive of a confounder rather than a real effect from particles or other pollutants and therefore would require a much better study design to support tacking action at a policy level with an expectation of a huge impact.

Fine to put filters into improve overall air quality but just not with the benefit rationale suggested in this study.

Install air filters in classrooms in Los Angeles has.

Places with clean outdoor air probably won't see much benefit.